380 
E. EAY LANKESTEB. 
pharyngeal coelom. Such a communication is suggested by 
Langerhans in his description of the capillary network on the 
caecum. I am inclined to think that there are not distinct 
capillaries and coelomic space around the caecum, but that the 
space is capillariform. 
Some main trunks of the vascular system of Amphioxus 
are obvious enough in sections. The difficulty is to make out 
definitely their connections. We have (1) the cardiac or 
endostylar aorta, a highly contractile vessel lying in the wide 
coelomic space below the hypobranchial ridge or endostyle of 
the pharynx. Anteriorly this vessel dilates into the “ heart” 
of Langerhans, placed just below the sphincter oris. From 
this “ heart” are given off anteriorly a right and left vessel to 
the oral tentacles, and laterally a single right so-called 
“ aortic arch,” a large sinuous vessel, which runs forward and 
upwards in the right prseoral epipleur (right side of oral hood), 
until it reaches the level of the notochord, where it joins 
(according to Langerhans) the right “ dorsal aorta.” This 
sinuous aortic arch has been described by Rolph as a gland, 
and in fact it appears to occupy the space in which a glandular 
structure is developed in the larva. 
The dorsal aortse are two vessels, right and left, underlying 
the notochordal sheath, and placed on either side of the 
hyperbranchial groove (see PI. XXXVI). They extend through- 
out the length of the perforated pharynx, but unite to form a 
single “posterior aorta” at the point where the alimentary 
canal narrows and becomes intestine. This single median 
vessel can be traced on the dorsal surface of the intestine 
as far as the anus, beyond which point it appears to be 
continued as a canal in the ventral part of the sheath of 
the notochord, finally ending blindly near the extremity of 
that organ. Similarly in the anterior region of the body 
the left aorta is continued forward in front of the mouth 
as a narrow canal in the left side of the notochordal sheath, 
and finally, I am inclined to think, opens into the cavity of 
one of the cephalic myotomes, the cavitary structure of the 
mesoblastic somites surviving from the embryonic condition 
